Air conditioning system



Jan. 6, 1942. w. L. M GRATH AIR CONDITIONING SYSTEM 2 Sheets-Shet 1 Filed July 25, 1958 WllllaM lliignl Jan. 6, 1942. w. L. M GRATH 2,269,280

' AIR'CONDITIONING SYSTEM Filed July 25, 1938 2 Sheets-Sheet 2 Patented Jan. 6, 1942 AIR CONDITIONING SYSTEM William L. McGrath, St. Paul, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application July 25 1938, Serial No. 221,066

21 Claims.

This invention relates in general to air conditioning and more particularly to-automatio controls for controlling the'operation of air conditioning apparatus and the supply of fresh air to a space being conditioned.

In air conditioning practice it has been customary to provide for automatically supplying fresh outside air to a space when the space requires cooling, and when the fresh air temperature is at a value which is suitable for coolin the space. in this manner it is necessary to control the amount of outside air supplied in order to prevent the temperature of the air being discharged into the space from becoming too low, due to the outside air being relatively low in temperature. One form 'of control arrangement for limiting the amount of fresh air supplied is by means of a thermostat located in the mixing chamber for the fresh and return air. This location for the thermostat however is not satisfactory in the average installation for the reason that there is usually no point in the mixing chamber in which the thermostat may be located to give a true indication of the average temperature of the mixture of fresh and return air. Due to stratification of the air within the mixing chamber, the temperature of the air contacting the thermostat will vary considerably, which causes the control apparatus to hunt and to operate unsatisfactorily in supplying air to the space at the desired value. In order to avoid the disadvantage of locating the controlling thermostat in the mixing chamber, in some cases the thermostat has been located so as to respond only to the temperature of the fresh air. This arrangement also'has ,not proved to be entirely satisfactory due to the fact that the supply of fresh air is not entirely dependent upon the damper position but also is dependent upon wind velocity and direction. Thus for varying wind velocities this location of the thermostat will allow the discharge temperature to ,vary correspondingly. I

It is an object of this invention to provide a fresh air damper control arrangement which will positively control the proportions of fresh and return air in a manner to maintain the tempera' ure of the discharge air at the desired value .for cooling the space. This result is obtained by locating thethermostat for the dampers in the discharge duct leading to the space to be conditioned, thereby measuring the temperature of the air actually being supplied to the space.

This thermostat is prevented from being influ- In providing for cooling the space enced by the usual heating coil by an interlocking of operation before the fresh air damper is opened beyond its minimum position.

It is therefore an object of this invention to provide afresh air damper control arrangement which varies the position of the dampers in a manner to prevent the temperature of the air being discharged to the space from falling below 'a predetermined value, and which is interlocked with the control for the air conditioning apparatus in a manner normally to place this apparatus out of operation before more than the minimum supply of fresh air is admitted to the space.

Another object of this invention is the provision of an air conditioning control system in which-the air conditioning apparatus is con-v trolled conjointly by a space condition responsive device and by a discharge air condition re-' sponsive limit control, and in which the action of the limit control is varied in accordance with variations in the space condition being controlled.

More specifically it is an object of this invention to provide a heating control system in which the heating device is controlled by a space thermostat, and a discharge limit control, and in which the discharge limit control is influenced in a manner to maintain the. discharge temperature at a relatively high value when the space is not overheated, while maintaining the discharge temperature at a lower value when the space is overheated.

A further object of this invention is the provision of anair conditioning control system which controls the air conditioning apparatus and the admission of fresh air to the space in a manner to maintain only a minimum supply of fresh air for ventilation purposes when the condition of the'space requires operation of the air cond tioning apparatus, which operates to maintain the air conditioning apparatus out of operation and to vary the supply of fresh air in a manner to maintain desired conditions within the space when operation of the conditioning apparatus is not required, and which automatically-replaces the air conditioning apparatus into operation in the event that the condition of the airdischarged into the space deviates from predetermined value.

Other objects of this inventilpn will become;

apparent from the following description and appended claims.

For a full disclosure of my invention reference is made to the following detailed descriptionand to the accompanying drawings in which Figure 1 illustrates diagrammatically one form of my invention, and in which Figure 2 illustrates diagrammatically modification.

Referring to the drawings reference character I indicates an air condition or heating chamber having a return air duct 2 which conveys air from the space to be heated to the chamber I. This chamber I is also connected to a fresh air inlet duct 4. The discharge end of chamber I is connected to a fan 5 which in turn is connected to discharge air into the space 3 through a discharge duct 6. Located within the chamber is a heating coil 1 which may be of any suitable type. This coil 1 is connected to a heating medium supply pipe 8 having a control valve 9 interposed therein. The valve 9 is actuated by means of a proportioning motor II] which may be of the type shown and described in the Taylor Patent 2,028,110 issued January 14, 1936. The proportions of fresh and return air supplied to the chamber I are controlled by means of a fresh air damper II and a return air damper l2. These dampers are of usual form and are cross. connected by a link 13 in a manner to cause simultaneous movement of these dampers in opposite manners. These dampers are actuated through any suitable linkage by means of a proportioning motor l4 which also may be of the type disclosed in the Taylor patent. The proportioning motors I and I4 are controlled by means of a return air controller l5 and discharge air controllers l6 and I1.

Referring to the return air controller l5, this controller may be of any desired type and is illustrated diagrammatically as including a bellows l8 which is connected by a capillary tube l9 to a control bulb located in the return air duct 2. The bellows l8 may actuate a bell crank member including an actuating arm 2| and a slider 22 which cooperates with a resistance 23 and a contact strip 24 for forming a control potentiometer. This controller.also includes a slider 25 which cooperates with a resistance 26 and a contact strip 21 for forming a second control potentiometer. This slider 25 is actuated in unison with the slider 22 by the bellows ill in any suitable manner such as by an insulated link 28. The actuating arm 2| of this controller is biased against the bellows l8 by means of a spring 28 for thus causing movement of the sliders 22 and 25 to the left upon contraction of bellows l8 due to fall in temperature at control bulb 20. It will be understood that as the return air temperature increases the pressure within bellows I8 will increase for causing movement of sliders 22 and 25 to the right against the action of spring 28. This instrument may be so designed and adjusted as to cause the slider 22 to engage the left hand end of resistance 23 and the slider 25 to engage the left hand end of contact strip 21 when the space temperature is at 69 F. or below. As the space temperature increases above 69 F. the slider 22 will move to the right along resistance 23 while the slider 25 will slide along contact strip 21. When the return air temperature reaches 71 F. the slider 22 will engage the right hand end of resistance 23 and the slider 25 will engage the left hand end of resistance 26. Upon further increase in temperature, the slider 22 will slide along contact strip 24 while the slider 25 will slide along resistance 26 and will engage the right hand end of this resistance when the return air temperature rises to 73 F.

Referring to the discharge controller [6 this controller may be similar to the return air controller I 5 and includes a bellows 30 which is connected by a capillary tube 3| to a control bulb 32 located in the discharge duct 6. This bellows 30 actuates a slider 33 which cooperates with resistance 34 and contact strip 35 to form a first control potentiometer, and also actuates a slider 36 whichcooperates with resistance 31 and contact strip 38 to form a second control potentiometer. This instrument may be so designed and adjusted as to cause the slider 36 to engage the left hand end of resistance 31 when the discharge air temperature is at 66 F. or above. At this time the slider 33 will engage the left hand end of contact strip 35. As the discharge air temperature falls between 66 F. and 63 F. the slider 36 will move to the right along resistance 31 and the slider 33 will move to the right along contact strip 35. When the discharge air temperature falls to 63 F. the slider 36 will engage the right hand end ofresistance 31 and the slider 33 will engage the'left hand end of resistance 34. Upon decrease in temperature below 63 F. the slider 36 will engage the left hand end of contact strip 38 and the slider 33 will engage the left hand end of resistance 34. Upon decrease in temperature below 63 F. the slider 33 will move to the right along resistance 34 and will engage the extreme right hand end of this resistance when the discharge temperature falls to F.

The discharge controller ll includes a bellows 39 which is connected by a capillary tube 40 to a controlbulb 4| located in discharge duct 6. This bellows 39 actuates a bell crank lever including an actuating arm 42 and a slider-43 which cooperates with a resistance 44 for forming a control potentiometer. This instrument may be designed and adjusted in a manner to cause the slider 43 to engage the left hand end of resistance 44 when the discharge temperature is at or above 69 F. As the discharge temperature falls below 69 F. the slider 43 will move to the right along resistance 44 and will engage the right hand end of this resistance when the discharge temperature falls to 67 F.

Upon reference to the Taylor patent it will be found that the proportioning motor I4 is adapted to assume intermediate positions in accordance with variations imresistance applied to the motor control circuit. This motor includes a threewire control circuit and is provided with control terminals marked R, W, and B. When equal values of resistance are connected across terminals R and W and terminals R and B this motor will assume mid position. However, if the resistance between terminals R and W is decreased without corresponding decrease in resistance across terminals R and B, the motor will rotate in a manner to close fresh air damper II and open return air damper l2 an amount proportionate to the change in resistance. if the resistance between terminals R and B is decreased without corresponding decrease in resistance connected across terminals R and W, the motor will rotate in the opposite direction for opening fresh air damper II and closing return air damper I 2 an amount proportionate to the change in resistance.

Referring now to the wiring between motor l4 and the controllers l5 and I6 it will be noted that terminal B is connected by wires 45 and 46 to the right hand end of resistance 26, while terminal W is connected to the contact strips 21 and 38 by means of wires 41, 48, and 49. Terminal R is connected by wire 50 to the slider Also '25 and 36 in the positions shown a circuit is completed from terminal R through wire 56,

. slider 36, wire slider 25, contact strip 21, wire 48, wire 41, and rheostat 52 to terminal W. Thus except for the resistance of rheostat 52, a shorteircuit is' completed between terminals R and W. This substantial short-circuit between terminals R and W without corresponding short-circuit between terminals R and B has caused'the motor I4 to assume a position in which the fresh air damper II is almost closed and in which return air damper I2 is almost wide open. The setting of the rheostat 52 now determines the amount of resistance between terminals R and W and therefore provides an adjustment for varying the minimum amount of fresh air supplied to the space. Thus as rheostat 52 is adjusted for decreasing its resistance, the motor I4 will rotate for closing damper II further and will completely close this damperwhen the rheostat 52 is adjusted for zero resistance. By adjusting rheostat 52 any desired minimum fresh air supply may be provided.

If the space temperature begins rising above 71 F. the slider will begin moving to the right across resistance 26. This will insert a portion of the resistance 26 into the circuit between terminals R and W and will also decrease the portion of the resistance 26 which is connected between terminals R and B by means of wires 45 and 46. Due to this increasing of the resistance between terminals R and W and decreasing of the resistance between terminals R and B, the motor I4 will rotate in a direction for opening damper II an amount proportionate to the movement of slider 45 along with resistance 26. When the space temperature rises to 13 F. the slider 25 will engage the right hand end of resistance 26 which will complete a circuit from terminal R, wire 50, slider 36, wire 5|, slider 25,

and wires 46 and 45 to terminal B, thus establishing a short-circuit between terminals R and B. At this time-the entire resistance 26 will be connected between the slider 25 and terminal W.

This short-circuit of terminals R and B and insertion of resistance 26 between terminals R and W will cause the motor I4 to'move to its.

extreme position for opening the fresh air damper II wideand closing the return air damper I2 completely. From the description thus far it should be apparent that when the discharge temperature is above 66 F. the thermostat I5 will vary the position of the dampers I I .and I2 in accordance with variations in return air or space temperature, the fresh air damper I I being closed to its minimum position when space temperature is at or below 71 F. As the space temperature increases above 71 F. however the freshair damper is opened and reaches wide open positionwhen the space temperature rises to 73 F.

As pointed out. above when the return air temperature is above 73 F. and the discharge air temperature is above 66 F. a short-circuit is completedv from terminal R through wire 5|],

slider 36, wire 5|, slider 25, and wires 46 and to terminal B. At this time the entire resistportion of. this resistance which is connected between terminals R and W. This increasing of resistance between terminals R and B and decreasing of resistance between terminals R and W will cause the motor I4 to rotate in a direction for closing fresh air damper II and opening return airdamper I2 an amount proportionate to the movement of slider 36 on resistance 31. When the discharge temperature falls to 63 F. the entire resistance 31 will be connected between terminals R and B,- and terminals R and W will be substantially short-circuited except for the resistance 49a interposed in wire 49 for causing the fresh air damper I I to assume substantially its minimum position. The purpose of resistance 49a is to prevent the damper II. from being robelow 63 F. the fresh air damper II will assume its minimum position for supplying no more fresh air than is necessary for ventilation. However,

if the space temperature should rise above 71 F.

thus indicating that cooling is necessary the fresh air damper I I will open an amount proportionate to the rise in space temperature above 71 F., thus admitting additional fresh air for cooling the space. If this increase in supply of fresh air should result in the discharge temperature falling below 66- F. the controller I6 will act to cause closing of the damper II an amount sufficient for preventing the temperature of the discharged air from falling too low, thus avoiding cold drafts upon the occupants within the space.

It should be noted that a resistance 53 is connected across wires 45 and 50, the purpose of this resistance is to balance out the control circuit for motor I4. This resistance should be of the same values as the control resistances 26 and 31.

Referring now to the contr'ols for the steam valve proportioning motor II) this motor is controlled by the conjoint action ,of the return air thermostat I5, the discharge air thermostats I6 and I1, and by means of an auxiliary switch 54 which is actuated by the fresh air damper motor I4. This auxiliary switch 54 is illustrated as diagrammatically comprising a lever 55 which actuates a mercury switch 56, this lever being actuated by the proportioning motor shaft. When the fresh air damper II assumes its normal minimum position the lever 55 will engage switch 56 for tilting it to bridge its left-hand electrodes, while when the fresh air damper II is away from the minimum position: the switch 56 will be tilted for bridging its right-hand electrodes.

With the controllers I 6 and I1 and the fresh air dampers II in the positions shown, terminal R of motor I0 will be directly connected to the slider 22 of the return air thermostat I5 as follows: terminal R, wire 51, slider 33, wire 58, left hand electrodes of mercu y switch 54, wire 59,

slider 43, and wire 60 to slider 22. The left hand end of the resistance 23 it will be noted is connected by wires 60', BI, and 62 to terminal B of motor l while the contact strip 24 is connected by wires 63 and 64 to terminal W of motor 10. It should also be noted that the resistance 34 is connected by wires 65 and 6-2 to terminal B. Consequently the entire resistance 34 at this time is connected across terminals R and B of motor Ill. Also the right hand end of resistance 44 is connected by wires 66, BI, and 62 to terminal B thus placing this entire resistance between terminals R and B of motor In. Thus with the controllers I6, l1, and 54 in the positions shown resistances 34 and 44 are connected across termiand contact strip 24 is connected by wires 63 and 64 to terminal W. The slider 22 therefore acts at this time to vary the portions of resistance 23 which are connected across terminals R and W and terminals R and B. With controller [5 in the position shown the space temperature is at approximately 70 and the slider 22 is engaging the center of resistance 23. This causes the resistance 23 to be equally divided between terminals R and W and terminals R and B thus causing the proportioning motor 10 to assume mid position in which the valve 9 is half open. If the space temperature should decrease the slider 22 will move to the left across resistance 23 thus decreasing the portion of this res stance which is connected between terminals R and B and increasing the portion of this resistance which is connected between terminals R and W. This will cause the proportioning motor ID to rotate in a direction for opening valve 9 an amount proportionate to the fall in space temperature. Upon an increase in space temperature the slider 22 will move to the right across resistance 23 for decreasing the portion of resistance 23 connected between terminals R and W and increasing the portionof this resistance which is connected between terminals R and B, thus causing motor ID to rotate in a direction for decreasing the supply of heating medium to the heater 1.

During mild weather the internal heat gain within the space 3 may cause the space temperature to rise sufliciently for causing thermostat l5 to-close valve 9 to such a point that the temperature of the air being discharged into the space falls below the setting of the discharge thermostat 'H. In such event the slider 43 will begin moving to the right across the resistance 44 thus inserting a portion of this resistance 44 into circuit with the slider 22 of controller 15. This will also decrease the portion of resistance 44 which is connected between terminals R and B due to the fact that the right hand end of resistance 44 is connected to terminal B by wires 66, BI, and 62. This increasir of resistance between terminals R .and W and decreasing of resistance between terminals R and B will cause the motor Ill to operate in a direction for open ing valve 9 an amount proportionate to the movement of slider 43 on resistance 44. From the motor l0 under the control of the return air controller I5 and the discharge low limit controller II. Thus when the space temperature is below 71 F. only a minimum amount of fresh air is supplied to the space and the supply of heat to the heater 1 is controlled in accordance with space temperature by the thermostat I5 and the discharge temperature is prevented from falling below 67 F. by means of the low limit controller I1.

In the event that spacev temperature should become excessive due to mild weather or due to a large heat gain within the space being, heated, the sliders 22 and 25 of the thermostat l5 will move to the right for causing the slider 25 to engage resistance 26 and the slider 22 to engage contact strip 24. At this time the fresh air damper II will remain at its minimum position due to the slider 25 merely engaging the left hand end of resistance 26. Due to the slider 22 engaging the contact strip 24, the thermostat l5 will tend to maintain the valve 9 closed, and the closing movement of valve 9 will be now controlled entirely by the low limit discharge thermostat I1. This thermostat will act to maintain the discharge temperature at approximately 68 F.

Upon continued rise in space temperature, the slider 25 of thermostat 15 will begin sliding to the right across resistance 26 which will cause movement of the fresh air damper H away from its minimum position thus increasing the flow of cool outside air into the space being conditioned. When the damper H is moved away from its minimum position, the mercury switch 56 will be tripped for breaking the circuit through its left hand electrodes and completing a circuit through its right hand electrodes. This will cause terminal R of motor I0 to be directly connected to terminal W as follows: terminal R,

wire 51, slider 33 contact strip 35, wire 58, right hand electrodes of switch 56, wire 61, and wire 64 to terminal W. Due to the unbridging of the left hand electrodes of mercury switch 56, the circuit from terminal R of the motor to the slider 43 of thermostat I! will be broken. Therefore the tilting of mercury switch 56 for bridging its right hand electrodes closes the valve 9 and disconnects the low limit thermostat I! from the valve motor circuit for preventing this thermostat from tending to open said valve. Thus when the fresh air damper II is opened due to overheating within the space, the valve 9 will be closed for placing the heater 1 out of operation. At this time the fresh air damper II will be positioned in accordance with space temperature and its opening movement will be limited by the low limit thermostat IS n a manner to prevent the temperature of the air being dischar ed into the space from falling too low. When the space temperature rises to 73 F... or above, the thermostat l5 will tend to cause fresh air damper H to be wide open. At such time the damper II will be completely under the control of the low limit thermostat 16 which will maintain the temperature of the air being discharged into the space between 63 F. and 66 F. If the overheating occurs during relatively mild weather it will take a considerable amount of fresh air in order to reduce the mixture of fresh and return air to a value within the control range of slider 36 5 and resistance 31 of thermostat I6. As the outdoor temperature becomes colder a smaller proportion of fresh air will be necessary for cooling the discharge air to the desired value and the thermostat I6 will cause damper I I ,to close to I will cause the slider 36 to engage the right hand l end of resistance 31 which will cause the damper motor I4 to close the fresh air damper II to substantially its minimum position for supplying the air necessary for ventilation. Due to the action of resistance 49a, the thermostat I6 will be incapable of closing damper II to a point for tripping the mercury switch 56 to bridge its left hand electrodes. Consequently at this time the switch 56 will remain in position for bridging its right hand electrodes which maintains the 5 low limit thermostat I1 out of operation and consequently the valve 9 wi l remain closed.

In the event that the fresh air temperature is so low that it causes the mixture of the minimum supply of fresh air with the return air to fall 36 below 63- F., the slider 33 of thermostat I6 will begin moving. to the right along resistance 34. It will be noted that slider 33 is directly connected to terminal R. by wire 51, and the right hand end of resistance 34 is connected to termi- 35 nal B of motor III by wires 62 and 65. Thus when the slider 33 engages the left hand end of resistance 34 this entire resistance is connected between-terminals R and B of the motor I0. However, as the slider 33 travels to the right across resistance 34, it'interposes a portion of the resistance 34 into the short-circuit previously established between terminals R and W and decreases the portion of the resistance 34 which is corinected between terminals R and B. This will cause opening of the valve 9 for thus preventing the discharge temperature from falling below the setting of the controller formed of slider 33 and resistance 34. I

From the foregoing description it should begin apparent that when th space temperature is between 69 F. and 71 F. the damper II will be closed to its minimum position for supplying only air necessary for ventilat on and the position of valve 9 will be controlled by the space thermostat ing below the setting of thermostat I'I. However, 50

when the space temperature rises above the setting'of the control range of the first potentiometer of thermostat I5, the second potentiometer of this thermostat will cause opening of the fresh air damper II beyond its minimum position which will immediately trip the mercury switch 56 for placing the low limit controller I! out of" operation and maintain the valve 9 completely closed. At this time the opening movement of the damper II will be determined by the second potentiometer of the thermostat I5 for supply-. ing the necessary amount of cold outside air to the space for cooling. the space, and the opening movement of damper' II will be limited by the charge temperature from falling to a value which would cause cold drafts within the space. In.

the event that the overheating occurs in relatively cold weather, the mixture of the minimum air supply for ventilation with the return air may causethe discharge temperature to fall to a point requiring heating in order to prevent cold drafts within the space. 11' tnishappens the second potentiometer or thermostat IE will cause opening of the valve the proper amount for maintaining the discharge temperature at a proper value. Thus when the system is in normal operation only a mimmum amount'of fresh air for ventilation is supplied and the discharge temperature is maintained relatively high by discharge thermostat l1. However, when the space becomes overheated the air for cooling the space is supplied and the thermostat I1 is placed out of operation for thus permitting the discharge temperature to be lowered for cooling the space. However, ifthe discharge temperature falls too vlow the thermostat It causes reopening of the valve 9 for thus preventing cold drafts to be caused within the space. It will therefore be seen that when the space temperature is at a proper value th discharge temperature is prevented from falling below a relatively high value, while when the space temperature becomes too high, the low limit discharge control apparatus is influenced for permitting the discharge temperature to fall to a lower value. In other words, the setting of the low limit discharge control apparatus is lowered when the space temperature becomes too high. I

Figure 2 Referring now to Figure 2, this figure shows a modified form of control system for obtaining the same results as the system of Figure 1. In this figure the supply of heating medium to the heating coil I01 is controlled. by a valve I09 posie.

tioned by a proportioning motor 'I I0. Also the dampers III and H2 are positioned by means of a proportioning motor II4. These motors III) and II4 are controlled by means of a space thermostat II5, a discharge thermostat H6, and a discharge thermostat II'I.

The return air or-space thermostat IIB comprises a bellows II8 which is connected by a capillary tube II9 to 'a control bulb I20 located in the return air duct I02. This bellows actuates a bell crank lever including an actuating arm I2I and a slider I22 which cooperates with the resistance I23. This instrument may be so designed and adjusted as to cause the slider I22 to engage the left hand end of resistance I23 when the space temperature falls to 69 F. When the space temperature increases to 71 F. the slider I22 will engage the right hand end resistance 'II. This controller II5 also includes an auxiliary switch I25. This witch I25 is illustrated diagrammatically as including a pivoted switch carrier I26 upon which is mounted a mercury switch I21. The switch carrier I26 is actuated by the actuating arm I2I in a manner to permit switch I21 to be tilted to open position whenever the space temperature is below 71 F. However, when the space temperature rises to 71 F. the slider I22 will engage the right hand end of resistance I23, and the actuating arm I 2] will engage switch carrier I26 for tilting the mercury switch I21 to closed position.

The discharge controller H6 is exactly the same as the discharge contro ler I6 of Figure 1.. thermostat I6 in a manner to prevent the dis- 75' This controller includes a s der I36 which cooperates with resistance I31 and contact strip I30 for forming a nrst control potentiometer, and slider I33 which cooperates with resistance I34 and contact strip I35 for forming a second con- I54 and I55 and with on contacts I56. and

I51. The left hand end of relay coil II is connected by a wire I58 to a transformer-secondary I59, while the right hand end of coil I5I is connected by wire I60 to the mercury switch I21.

This mercury switch is also connected by wire I6I to the transformer secondary I59. Thus when the mercury switch I21 is closed due to the space temperature reaching 71 F., the relay coil I5I will be energized for causing switch arms I52 and I53 to engage in contacts I54 and I55. When the space temperature is below 71 F. the mercury switch I21 is tilted to open position for deenergizing relay coil I5I which permits switch arms I52 and I53 to engage out" contacts I56 and I51.

Referring now to the wiring for motor ,4, terminal R of. this motor is connectedby wire I62 to the switch arm I52 of relay I50. Terminal W of motor R is connected through rheostat I64 and wire I65 to contact I56 of relay I50 and also by wire 166 to the contact strip I38 of thermostat II6. The resistance I31 of this thermostat is directly connected to terminal B of motor II4 by wire I61. The contact I54 of relay I50 is connected by wire I68 to the slider I36 of thermostat II6.

When the space temperature is below 71 F. for causing the relay I50 to be deenergized, the switch arm I52 will engage contact I56 as shown which will complete a circuit from terminal R of motor I I4 through wire I62, switcharm I52, con-- tact I56, wire I65, and rheostat I64 to terminal W. This will therefore short-circuit terminals R and W except for the minimum position rheostat I64, and therefore will cause the motor II4 to close fresh air damper to a minimum position as determined by the setting of rheostat I64. Therefore when the space temperature is below 71 F. the fresh air damper is caused to be closed to its minimum position by the action of the 4 auxiliary switch I25. However, if the return air or space temperature rises above 71 F. the auxiliary switch I25 will energize relay I50 for causing switch arm I52 to engage contact I54. This will complete a circuit from terminal R of the motor through wire I62, switch arm I52, contact I54, and wire I68 to the slider I36. of thermostat II6. Due to switch arm I52 no longer engaging contact I 56 the short-circuit previously established between terminals R and W will be broken and consequently the thermostat II6 will be placed in control of the damper motor II4. This thermostat II6 will now control the damper III in the same manner as the thermostat I6 of Figure 1 controls the damper II. In other words, when the discharge temperature is at 66 F. or above, the thermostat I I6 will cause the damper III to be wide open. However, as the discharge temperature falls, the thermostat II6 will cause throttling'of damper III in a manner to mainta'in the discharge temperature within the control range of this thermostat.

Referring now to the controls for the valve motor IIO it will be noted that terminal B of this motor is connected by wires I10, I1I, I12, I13, and I14 to the right hand end of resistance I44, to the right hand end of resistance I34, and to the left hand end of resistance I23. Terminal R of this motor is connected by wire I15 to the switch arm I53 and the contact I51 is connected by wire I16 to the slider I43 of thermostat H1. The left hand end of resistance I44 is connected by wire I11 to the slider I33 of thermostat H6 and is also connected by wire I18 to the contact I55 of relay I50. The contact strip I35 of thermostat H6 is connected by wire I19 to the slider 122 of the thermostat II5. When the relay I50 is deenergized and the discharge temperature is above 69 F. terminal R of motor IIO will be directly connected to slider I22 of thermostat 5 as follows: terminal R, wire I15, switch arm I53, contact I51, wire I16, slider I43, wire I11, slider I33, and wire I19 to slider I22. The right hand end of resistance I23 of thermostat H5 is connected by wire I to terminal W of motor IIO. Thus with the parts in the positions shown, the thermostat H5 is in complete control of the position assumed by the motor IIO. If the space temperature should decrease, the slider I22 will shift to the left along resistance I23 thus decreasingthe portion of this resistance which is connected between terminals R and B and increasing the portion of resistance I23 which is connected between terminals R and W, thus causing motor IIO to open valve I09 for increasing the supply of heating medium to coil I01. Upon an increase in space temperature the opposite action will occur for closing valve I09 to reduce the supply of heating medium to coil I01. In the event that the closing of valve I09 by thermostat I I5 causes the discharge temperature to fall below the setting of the discharge thermostat II1, the slider I43 of this controller will begin moving to the right across resistance I44, thus inserting a portion of this resistance between terminal R of motor H0 and the slider I22, thermostat H5, and also decreasing the portion of this resistance which is connected between terminals R and B of motor IIO by wires HI and I10. This will cause motor IIO to reopen valve I09 an amount sufficient to maintain the discharge temperature within the control range thermostat I I1. From the description thus far it should be apparent that as long as the space temperature is below 71 F. the auxiliary switch I25 will be open which positions the .relay I50 for placing the valve 0 under the control of the return air thermostat H5 and the discharge thermostat II1. These thermostats will now control valve I09 in a manner to prevent the space temperature from falling below the setting of thermostat H5 and the discharge temperature from falling below the setting of thermostat II1.

If the space temperature rises above 71 F. the auxiliary switch I25 of thermostat II5 will be closed for energizing relay I50 thereby bringing switch arm I53 into engagement with contact I55. Due to the switch arm I53 now being disengaged from contact I51, the connection between terminal R of motor H0 and the slider I43 of thermostat II1 will be broken and consequently this thermostat will be rendered inoperative to control motor I I0. Due to engagement of switch arm I 53-with contact I55, terminal R of motor IIO will now be connected by wire I15, switch arm I53, contact I55, wire I18, and wire I11 to the slider I33 of thermostat IIG. As long as the discharge temperature is above 63 F. the slider I33 of thermostat IIG will engage the contact strip I35 which will complete the circuit from terminal R through wire- I19, slider I22, and wire I80 to terminal W of motor I09 thus short-circuiting terminals R and W of this motor. This will cause motor I I to close valve I09 completely. However, if the discharge temperature falls below 63 F. due to the outside air being cold, the

slider I33 of thermostat II6 will begin traveling to the right across resistance I34. This resistrequired. In addition it will be apparent that both forms of my invention provide for maintaining the discharge temperature at a relatively high value as long as the space is not overheated I and provide for lowering the temperature of the discharged air when the space becomes overheated. In other words, in both cases, the setting of the discharge temperature responsive means is lowered when the space becomes overheated. Also both forms of my invention provide for placing the heater in operation even when the space is overheated, in the event that ance I34, it will be noted, is connected by wires I13, I12, and I10 to terminal B of motor IIO. Thus as slider I33 travelsto the right across resistance I34, it decreases the portion of resistance I34 which is connected between terminals R and B and also inserts a portion of resistance I34 into the short-circuitpreviously established between terminals R and W. Therefore motor IIO will be caused to open valve I09 an amount proportionate to the travel of slider I33 to the right across resistance I34.

Referring now to the operation of the complete system it should be. noted that when the space temperature is below 71 F. the auxiliary switch outside temperature is so low as to cause the minimum supply of fresh air to overcool the air being discharged to the space.

While for the purpose of description specific values of temperature have been referred to, it will be understood thatthese values may be varied as desired for different applications and installations of my improved control system. Also while I have shown and described only two possible forms of my invention it will be apparent that many modifications and adaptations which are within the scope of my invention will occur to I25 of thermostat II5will be open for deenergizventilation purposes will be provided, and the valve I 09 will be controlled by thermostat H5 and thermostat H1 in a manner to prevent the space temperature from falling below the setting of thermostat H5 and the discharge temperaturefrom fallingbelow the setting of thermostat II1. However, when the space temperature rises above 71 F. the thermostat II5 will tend to close the valve I09 completely and will also cause closing of the auxiliary switch I25 which energizes relay I50 for placing the fresh air damper motor II4 under the control of discharge thermostat IIS and for rendering the discharge thermostat II1 incapable ofopening valve I09 when the discharge temperature falls below the setting of this thermostat. The valve I09 will therefore 'beentirely closed and the damper III will be positioned by thermostat II 6 in a manner to maintain the temperature of the air being discharged into the space between 66F. and 63 F. In the event that the outside temperature is low when the overheating occurs, the mixture of the minimum supply of fresh air with the return air may cause the temperature of the air passing to the space to fall below 63 F. even though the thermostat I I6 has positioned damper III to its minimum position. If this occursthe slider I33 of thermostatIIG in engaging the resistance I34 will reopen the valve I09 for thus adding heat to the air for preventing the discharge temperature from falling too low.

It will be apparent that both forms of my invention provide for automatic control of the fresh air damper and the heater for maintaining proper conditions within the space, and provide only the necessary air for ventilation when heating of the space is necessary, and in addition supply just the proper amount of outside air to the space for delivering air to the space at proper temperature to cool the space whenv cooling is those skilled in the art. I therefore desired to be 'limited only by the scope of the appended claims.

I claim as my invention:

1. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for heating the supply of fresh air, a first motor for controlling the heating means, a flow controller for controlling the supply of fresh air, a second motor for actuating the flow controller, thermostatic means influenced by space temperature for controlling said first andsecond motors in a manner to reduce the supply of fresh air and to increase the effect of said heating means upon fall in space temperature, discharge thermostatic means influenced by the temperature of the air passing to said space for controlling said first motor conjointly with the space thermostatic means, in a manner to prevent the temperature of the air passing to said space from falling below a predetermined value, and means actuated in accordance with said flow controller for lowering the setting of said discharge thermostatic means as the supply offresh air is increased above a predetermined value.

2. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for heating the supply of fresh air, a first motor for controlling the heating means, a flow controller for controlling the supply of fresh air, a second motor for positioning said flow controller, thermostatic means influenced by space temperature for controlling first and second motors in a manner to reduce the supply of fresh air and to increase the effect of said heatingmeans upon fall in space temperature, low limit discharge thermostatic means influenced by the temperature of the air passing to said space for controlling said first motor in for heating the supply of fresh air, a first motor for controlling the heating means, a flow controller for controlling the supply of fresh air, a second motor for position ing the flow controller, thermostatic means infiuenced by space temperature for controlling said first and second motors in a manner to reduce the supply of fresh air and to increase the effect of said heating means upon fall in space temperature, discharge temperature responsive means for cooperating in controlling. said heating means and said flow controller in a manner to prevent the temperature of the air discharged to said space from falling below a predetermined value, and means actuated in accordance with said flow controller for rendering said discharge temperature responsive means substantially incapable of placing said heating means in operation when said flow controller is positioned for permitting a predetermined fiow of fresh air to the space.

4. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for heating the supply of fresh air, a first motor for controlling the heating means, a flow controller for controlling the supply of fresh air, a second motor for positioning the fiow controller, thermostatic means influenced by space temperature for controlling said first and second motors in a manner to reduce the supply of fresh air and to increase the effect of said heating means upon fall in space temperature, low limit discharge temperature responsive means for cooperating in controlling said heating means and said flow controller in a mannerto prevent the temperature of the air discharged to said space from falling below a predetermined value, and means actuated upon space temperature reaching a predetermined high value for normally rendering said discharge temperature responsive means incapable of placing said heating means in substantial operation.

5. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for conditioning the supply of fresh air, a first motor for controlling said conditioning means, a flow controller forvarying the supply of fresh air, a second motor for positioning the flow controller, thermostatic means for controlling said first motor' in accordan'ce with the condition of the space, 10w limit thermostatic means responsive to the temperature of the discharge air for cooperating in controlling said first motor in a manner to prevent the discharge air temperature from falling too low, and switching means actuated by said space thermostatic means for actuating said second motor to restrict the flow of fresh air and to place said discharge thermostatic means in control of said conditioning means when said switching means is in oneposition, and to permit actuation of said second motor for increasing the flow of fresh air while placing said discharge thermostatic means out of control of said first motor when said switching means is in another position. i

6. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for conditioning the supply of fresh air, a first motor for controlling said conditioning means, a fiow controller for varying the supply of fresh air, a second motor for positioning said flow controller, thermostatic means for controlling said first motor in accordance with the condition of the space, low limit ther- 'mostatic means responsive to the temperature of means is in one position, and to permit actuation of said second motor for increasing the fiow of fresh air and to vary the control of said discharge thermostatic means upon said first motor when said switching means is in another position.

7. In an air conditioning system, in combination, means for-supplying fresh air to a space to be conditioned, means for conditioning the supply of fresh air, a'first motor for controlling said conditioning means, a flow controller for varying the supply of fresh air, a second motor for positioning said flow controller, thermostatic means including a control device for controlling said first motor in accordance with the condition of the space, condition responsive means for controlling said second motor, and two-position switching means controlled by said space thermostatic means and separate from said control device for placing said second motor under the control of said condition responsive means when the switching means is in one position and for causing said second motor to reduce the fiow of air to a predetermined amount when said switching means is in another position.

8. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, means for heating the supply of fresh air, a first motor for controlling the heating means, a flow controller for controlling the supply of fresh air, a second motor for actuating the flow controller, thermostatic means influenced by space temperature for controlling said first and second motors in a manner to reduce the supply of fresh ai'rand to increase the 9. In an air conditioning system for a space,

in combination, a conditioning chamber, means demand for heat in said space for controlling said heating means in a manner to maintain a der sired temperature in said space, a thermostat the discharge air for cooperating in controlling 76 responsive to the temperature of the air'dis-= charged to said space connected to said flow control means, a relay in the connections between the discharge thermostat and said flow controlmeans and adapted in a first position to render the discharge thermostat operative to control said flow control means and in a secondlposition to place said discharge thermostat out of control of said flow control means and to cause said fiow control means'to reduce the flow of fresh air to at least a minimum, and control means for causing said relay to shift from its first position to its second position when operation of the heating means becomes unnecessary.

' ii). In an air conditioning system for a space, in combination, a conditioning chamber, means for passing air through said chamber and discharging it into said space, means for supplying fresh air to said chamber, flow control means for controlling the flow of fresh air, heating means for heating the air as it flows through the chamber, space thermostatic means responsive to the demand for heat in said space for controlling said heating means in a manner to maintain a desired temperature in said space, a thermostat responsive to the temperature of the air discharged tosaid space connected to said flow control means, a relay in the connections between the discharge thermostat and said flow control means and adapted in a first position to render the discharge thermostat operative to control said flow control means and in a second position to place said discharge thermostat out of control of said flow control means and to cause said flow control means to reduce the flow of fresh air to at least a minimum, and control means actuated by said space thermostatic means for controlling said relay in a manner to cause it to assume its first position when space value, and means responsive to a predetermined high space temperature for rendering said first controller incapable of increasing the heating effect when the temperature of said discharge air drops to said first predetermined value.

temperature rises to a value requiring cooling I and for causing it to assume its second position when the space temperature falls to a lower value.

11. In an air conditioning system for a space,

in combination, a conditioning chamber, means for passing air through said chamber and discontrolling the flow of fresh air, heating means for heating the air as it flows through the chamber, space thermostatic means responsive to the demand for heat in said space for controlling said heating means ina manner to maintain a desired temperaturejn said space, a thermostat responsive to the temperature of the air discharged to said space connected to said flow control means, a two-position control device in the connections between the discharge thermostat and said flow control means and adapted in a first position to render the discharge thermostat operative to control said flow. control means and in a second position to place said discharge thermostat out of control of said flow control means and tocause said flow control means to reduce the flow of fresh air to at least a minimum, and means for causing said control device to assume its second position when the heating means'is placed into operation and for causing said control device to assume its first position when the heating means is placed out of operation.

12. In a system of the class described, in combination, a heating means, means for passing air into contact with said heating means and for discharging it into a space to be heated, variable impedance means responsive to the temperature of the air in said space for controlling said heating means in a modulating manner, a first low limit variable impedance controller responsive to the temperature of the discharge air for additionally modulatingly controlling said heating means in a manner to increase the heating effect thereof independently of said space temperature responsive means when the temperature of said discharge airfalls below a first predetermined value, a second low limit variable impedance controller responsive to the temperature of the dis-.

charge air for modulatingly increasing the heat- 13. In a system of the class described, in combination, a heating means, means for passing air into contact with said heating ineans and for discharging it into a space to be heated, a first variable impedance controller influenced by the temperature of the air beingdischarged to said space for modulatingly controlling said heating means in a manner to prevent the temperature of the discharge air from falling below a predetermined value, a second variable impedance controller influenced by said discharge air for increasing the heating efi'ect of said heating means when the temperature of the discharge air enters a predetermined lower range of values, and space temperatureresponsive means for interrupting the control of said heating means by one of said controllers when the space temperature assumes a predetermined value. c

14. In a system of the class described, in combination, a heating means, means for passing air into contact with said heating means and for discharging it into a space to be heated, variable impedance means responsive to the temperature of the air in said space for modulatinglycontrolling said heating means in a manner tending to maintain a constant space temperature, low limit variable impedance means responsive to the temperature of the discharge air for modulatingly controlling said heating means in a manner to increase the heating effect thereof independently of the space temperature respondition responsive means.

sive means to thereby prevent the temperature of said discharge air from falling below the setting of said discharge air temperature responsive means, and means responsive to space temperature for varying the setting of said variable impedance discharge air temperature responsive means in accordance with variations in space temperature.

15. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, now control means for controlling the supply of fresh air, a condition changer for changing the condition of the air, a first motor for controlling said condition changer, condition responsive means located at the discharge of the conditioning system influenced by the condition of the air passing to said space for controlling said first motor, a second motor for actuating the flow control means, and means actuated in accordance with the operation of said second motor for varying the setting of said con- 16. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, flow control means for controlling the supply of fresh air, a condition changer for changing the condition of the air,- a first motor for controlling said condition "changer, a condition responsivedevice located atthe discharge of the conditioning system influenced by the condition of the air passing to said space for controlling said flrst motor, a second motor for actuating the flow control means, and means actl'iated in accordance with the operation of said responsive device in controlling said condition changer.

17. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, flow control means for controlling the supply of fresh air, a condition changer for changing the condition of the air, a first motor for controlling said condition changer, a condition responsive device located at the discharge of the conditioning system influenced by the condition of the air passing to said space for controlling said first motor, a second motor for actuating the flow control means, and means actuated in accordance with the operation of said second motor for placing said condition responsive device into and out of control relationship the supply of fresh air, a condition changer for' changing the condition 'of the air, a first motor for controlling said condition changer, a first condition responsive device for controlling said first motor, a second condition responsive device for controlling said first motor, a second motor for actuating the fiow control means, and means actuated in accordance with the operation of said second motor for interrupting the control of said condition changer by one of said condition responsive devices.

19. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, flow control means for controlling the supply of fresh air, heating means for heating said air, a first motor for controlling said heating means, temperature responsive means infiuenced by the heating means for controlling said first motor, a second motor for actuating the fiow control means, and means actuated in accordance with the operation of said second motor for controlling said temperature responsive means in a manner to vary the temperature maintained by said temperature responsive means in accordance with the action of said second motor.

20. In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, flow control means for controlling the supply of fresh air, heating means for heating said air, a first motor for controlling said heating means, a controller located at the discharge of the conditioning system influenced by the temperature of the air passing to said space for controlling said first motor, a second motor for actuating the flow control means, and means actuated by said second motor for placing said "controller into or out of operation.

21 In an air conditioning system, in combination, means for supplying fresh air to a space to be conditioned, fiow control means for controlling the supply of fresh air,heatlng means for heating said air, a first motor for controlling said heating means, a first temperature controller influenced by the temperature of the air passing to said space for controlling said first motor and hence said heating means in a manner to maintain the temperature of the air passing to said space above a predetermined value, a second temperature responsive controller influenced by the air passing to said spacefor controlling said first motor and hence said heating means ina manner to maintain the temperature or the air passing to said space above a predetermined lower value, a second motor for actuating the flow control means, and means actuated in accordance with the operation of said second motor for interrupting the control of said heating means by said first controller when said flow of fresh air is above a predetermined amount.

WILLIAM L. McGRATH. 

